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CONTENTS 



INTRODUCTION 



PAGE 



3 



PART I. GENETICS 



I. Darwin's Theory of Evolution and its Evidences 7 

 11. Contributions of Lamarck, Weismann, and Herbert 

 Spencer to the Theory of Evolution; Darwin's 



Theory of Pangenesis 18 



III. Are Acquired Characters Inherited .^ 28 



IV. Weismann's Theory of Heredity 47 



V. Attempts to Classify and Measure Variation : Biom- 

 etry b^ 



VI. The Mutation Theory 71 



VII. The Pioneer Plant Hybridizers : the Discovery and 



Rediscovery of Mendel's Law 82 



VIII. Mendel's Law of Heredity Illustrated in Animal 



Breeding 88 



IX. Some Mendelian Terms and their Uses 98 



X. Calculating Mendelian Expectations 104 



XI. Modified Mendelian Ratios; Heterozygous Char- 

 acters; Atavism or Reversion 109 



XII. The Unit-Characters of Rodents l^^a 



XIII. Unit-Characters in Cattle and Horses 130 



XIV. Unit-Characters in Swine, Sheep, Dogs and Cats 137 

 XVv Unit-Characters in Poultry and in Plants . . . 145 



XVI. Unit-Characters of Insects 154 



XVII. Sex-Linked and other Kinds of Linked Inheritance 



in Drosophila 159 



XVIII. Drosophila Type and Poultry Type of Sex-Linked 



Inheritance 164 



XIX. Linkage , 107 



XX. The Nature of Genes 177 



XXI. Are Unit-Characters (Genes) Constant or Variable? 182 

 XXII. Inheritance of Size and other Quantitative Char- 

 acters. The Hypothesis of Multiple Factors 190 



XXIII. Genetic Changes and the Chromosomes 205 



XXIV. Genetic Changes in Asexual Reproduction, in Par- 



thenogenesis, AND IN Self-Fertilization . . . 209 



vii 



